1. Field of the Invention
The invention relates to a drive unit for a twin-screw machine which can be driven in rotation in the same direction and the screw shafts of which have axial spacing.
As the screws mesh with one another in screw machines of this type, the axial spacing is much smaller than the external diameter of the respective screws. The screw shafts, which are generally in the form of spline shafts, therefore have merely a comparatively small spacing from one another, so the drive is generally provided by a drive motor via a correspondingly complex branching gear preceded by or associated with a reduction gear.
2. Background Art
It is already known from WO 03/095178 A1 to use a torque motor as a direct drive for a multi-shaft extruder rotating in the same direction. This torque motor in the form of a hollow-shaft motor has, on the internal circumference of its hollow rotor, inner teeth on which crown gears attached to the output shafts roll. The output shafts are supported, inter alia, in radial bearings arranged in the hollow rotor. The axial forces have to be absorbed in a different manner. This known solution is complex and can be used merely for relatively small extruders.
It is also known from the journal “Kunststoffe” September 2004 to drive single-screw extruders using torque motors.